Development and optimization of a laser carbonized polyimide film as a sensor substrate for an all-polymer humidity sensor - Polyimides and Other High Temperature Polymers - page 441

Figure 5. Change in sensor response at various HMPTAC coating thicknesses (in terms of µg/mm 2 )
and rates of change in relative humidity. 34.6 µg/mm 2 at 1.3% RH/min, 46.0 µg/mm 2 at 1.3%
RH/min, 34.6 µg/mm 2 at 51% RH/min, 46.0 µg/mm 2 at 51% RH/min.

ness increased from 5.7 µg/mm 2 to 17.2 µg/mm 2 . However, at a thickness of
22.9 µg/mm 2 , the sensor exhibited a dramatic increase in dynamic range from
22 95% RH. Curiously, this large increase was unique to the small

sensor area design. For sensors with wider spaced filaments (60

− 95% RH to 5 −

150 µm) or
greater sensor area (four or six fingered comb designs), the range remained con-
stant at 22

−

95% RH. A thickness of HMPTAC at 22.9 µg/mm 2 was optimal for
the small sensor design. Additional drop coating to increase the HMPTAC layer
thickness increased sensitivity only slightly, but greatly increased sensor response
time. This effect can be seen in Figure 5. These sensors showed little hysteresis
when the relative humidity was changed slowly (1.3% RH per minute) (Figure 6).
The sensors demonstrated a response time of 30 seconds for a step increase in
relative humidity from either 40% to 90% or from 90% to 40%.

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